1. Field of the Invention
The present invention is in the field of orthotics and specifically relates to an orthotic device that relieves some of the downward force on the user's lower spine when the user is seated.
2. The Prior Art
It has long been understood that most of the weight of the torso is transmitted to the pelvis through the spine, and that if this weight is reduced, for example by pulling upward on the torso, the pressure on the spinal dics and the nerves around them will be reduced, thereby reducing the pain that accompanies sitting.
An early approach to the problem was to provide a harness for suspending the torso from the back of a car seat. This was not satisfactory for users who needed to move from one location to another and from one seat to another.
A more recent approach is shown in U.S. Pat. No. 4,881,528 issued Nov. 21, 1989 to Scott. In Scott's device the seat is not part of the device, and this is certainly an improvement over earlier devices. Scott's device includes a rigid U-shaped frame the legs of which are about as far apart as the user's shoulder blades. This frame extends up along the user's back, and a girdle attached to the rigid frame pulls upwardly on the user's rib cage, thereby transferring some of the weight of the upper body to the rigid frame. The base of the frame rests on the seat.
This device is not entirely satisfactorily for the following reason. All parts of the user's body are located in front of the rigid frame, and therefore the center of gravity of any lifted weight must also lie in front of the rigid frame. To the extent that the device diverts some of the weight from the user's spine, to that extent a pitching moment is developed that tends to rotate the upper torso forward. The user must continually force his torso rearward if he wishes to sit up straight.
With this in mind, the present inventor set out to create a better device.